Conventionally, a fuel cell stack having a tubular fuel cell has been known as described in, for example, paragraph 0028 and FIG. 4 in Japanese Patent Laid-open Publication No. 2002-289249 and FIGS. 1 and 6 in Japanese Patent Laid-open Publication No. 5-101842. Now, referring to FIG. 11, an example of a conventional fuel cell stack described in the Japanese Patent Laid-open Publication No. 2002-289249 will be explained. FIG. 11 is a schematically cross-sectional view of a conventional fuel cell stack.
As shown in FIG. 11, a fuel cell stack 200 described in the Japanese Patent Laid-open Publication No. 2002-289249 has a structure in which a plurality of cylindrical fuel cells 202 are arranged laterally relative to a longitudinal direction thereof, and opposite ends of the fuel cells 202 are supported by respective metallic plates 204. In this fuel cell stack 200, the fuel cells 202 are electrically connected to each other in parallel.
The fuel cell 202 has an inner electrode layer 204, an outer electrode layer 208, and an electrolyte layer 206 disposed therebetween. On one end of the fuel cell 202, a connecting member 210 inserted inside of the inner electrode layer 204 is provided. On the other end thereof, another connecting member 212 fitted to outside of the outer electrode layer 208 is provided. The inner and outer electrode layers 204, 208 and the connecting members 210, 212 are connected by means of brazing, flame spraying or press fitting. Further, the connecting members 210, 212 and the metallic plates 204 are connected by means of welding, crimping or press fitting.
Further, FIGS. 1 and 6 in Japanese Patent Laid-open Publication No. 5-101842 shows a hollow hexagonal fuel cell, at an end of which an inner electrode is longitudinally exposed.
In the fuel cell stack 200 disclosed in Japanese Patent Laid-open Publication No. 2002-289249, it is difficult to attach the connecting member 210 to the inner electrode 204, and contact resistance therebetween tends to become large. Especially, it is difficult to attach the connecting member 210 to the inner electrode 204 of the fuel cell 202 having an outer diameter within 1-10 mm.
A voltage which can be generated by a single fuel cell is constant regardless of a size thereof. Thus, to obtain a high voltage, it is required that fuel cells be electrically connected to each other in a series. On the other hand, to obtain a large current, for example, fuel cells are connected to each other in parallel. Since a number of fuel cells connected to each other in a series or in parallel varies depending on the use thereof, a need for easily assembling fuel cells in desired electrical connections. In a fuel cell device incorporating the fuel cell stack 200 disclosed in Japanese Patent Laid-open Publication No. 2002-289249, one of the two following steps is needed, one step of electrically assembling a plurality of fuel cells 202 in a series and then electrically connecting the assembled fuel cells 202 in parallel to form a fuel cell stack 200; and the other step of electrically assembling a plurality of fuel cells 202 in parallel to form a fuel cell stack 200 and then electrically assembling the fuel cell stacks in a series. This means that assembling an entire fuel cell device takes a lot of trouble.
It is therefore an object of the present invention is to provide a fuel cell body, a fuel cell unit, a fuel cell stack and a fuel cell device including one of them, in each of which electricity can be easily taken out from the inner electrode layer, and fuel cells can be easily assembled with each other and connected to each other in electrically parallel and/or in a electrical series.